In recent years, improvement of processing ability of a mobile terminal device such as a mobile phone has resulted in multi-functionalization of a mobile phone. The mobile terminal device may perform various information processing, such as, for example, document creation, website access, e-mail transmission and reception, and moving picture reproduction. In most cases, the above-described mobile terminal device includes input keys to be used by a user to perform an input operation. For example, there is a mobile terminal device that includes a numerical keypad suitable for inputting numbers and a QWERTY keyboard suitable for inputting alphabets and other characters. The QWERTY keyboard may be called a full keyboard. In particular, the QWERTY keyboard, often used in a desk-top computer, is suitable for inputting sentences.
International Publication Pamphlet No. WO03/028346 discloses that a mobile terminal device having a keyboard. The mobile terminal device includes an extendible QWERTY keyboard on a lower layer under the numerical keypad. When the QWERTY keyboard is folded, the numerical keypad of this electronic device is exposed. Japanese Laid-Open Patent Publication No. 2007-179525 discloses that a three-stage stacked portable electronic apparatus with an upper case with a display unit, a middle case with a full keyboard, and a lower case with a numerical keypad. The full keyboard of the portable electronic apparatus is exposed when the upper case is rotated relative to the middle case. The numerical keypad of the portable electronic apparatus is exposed when the lower case is slid relative to the middle case.
A slide-type mobile terminal device, that is, a mobile terminal device with two housings e is realized by one of the housings sliding relative to the other housing. The slide-type mobile terminal device may have more than two housings. As for the above-described mobile terminal device, the input keys may be allocated in an area that is exposed when the housing is slid. However, the area that is exposed when the housing is slid is not large enough. This may decrease operability of key input. Another housing for allocating the input keys may be added. However, addition of the housing may decrease portability and operability of the mobile terminal device.